In a mug soften 1 tbsp of butter in microwave, about 5 seconds. You don’t want it melted, just soft. Stir in 2 tbsp of sugar and mix until well incorporated. Stir in applesauce, vanilla (just a tiny bit, we’re talking drops), flour, baking powder, and pinch of salt; stirring until just combined. Use the back of your spoon to smooth it out in the bottom of the mug.
Want struesel? Of course you do! In a separate, small bowl, combine 1 tbsp of butter, 2 tbsp of flour, 1 tbsp of brown sugar, and ¼ tsp cinnamon. Use your fingers to to pinch the butter and mix it in with the other ingredients. When it starts to look like lumpy sand (appetizing, eh?) and all ingredients are combined, pour on top of cake batter in mug.
Cook in the microwave for 50-80 seconds depending on your microwave. At 1 minute, my microwave cooks it perfectly. It will look just barely set on top. You don’t want to overcook it and things tend to get ugly fast in the microwave. I suggest cooking it 50 seconds, and then in 10 second intervals checking after each interval until done. Eat white it’s still warm. Once it cools off, it tends to loose some of it’s magic!